1. Field of the Invention
The present invention relates generally to an improved host system within a network and in particular to an improved failover in a host with multiple adapters enabled to concurrently support multiple virtual Internet Protocol (IP) addresses (VIPAs).
2. Description of the Related Art
The Address Resolution Protocol (ARP), used in Transport Control Protocol/Internet Protocol (TCP/IP) networks, such as the Internet, provides a mapping between an IP address and a media access control (MAC) address to a requesting host. In one example, a requesting host which needs to learn the MAC address for a given IP address broadcasts an ARP request containing the IP address to all routers and hosts in a network. Adapters at the hosts receive the requests. The adapter assigned the IP address responds to the ARP request with an ARP reply including the MAC address corresponding to the IP address. Thus, the requesting host learns the MAC address corresponding to the IP address through an ARP reply to an ARP request.
A “real” IP address is one that is associated with a physical adapter. An adapter often supports thousands of network sessions with other hosts. If the adapter fails, all of the active sessions using the IP address associated with the adapter will also fail. Virtual IP addresses (VIPAs) were conceived to mitigate this problem, A VIPA is an IP address that is associated with a host, rather than with a physical adapter. Messages can be addressed to real IP addresses or to VIPA. If a host contains multiple adapters, IP traffic addressed to a VIPA can be routed through any of the adapters. In this way, a host can provide fault tolerance after an adapter failure by routing the VIPA traffic over a different physical adapter.
A VIPA based failover system, however, is still limited in efficiency if more than one VIPA is assigned to a single host. In particular, white a single VIPA may be supported across multiple adapters, if multiple VIPAs are assigned by a host, each VIPA requires a separate set of adapters assigned solely to that VIPA. Separately assigning multiple adapters to each separate VIPA, however, may require assigning a separate backup adapter to each VIPA to facilitate failover in the event of an adapter failure. Assigning a separate backup adapter to each VIPA is an inefficient allocation of resources.